Quantum attacks worry computer scientists

Today's network admins have it easy

In the weird world of quantum computing, the state of computer systems networked together is so fragile that a read access to a single quantum bit, or qubit, on one machine would require a network-wide reset.

It's no wonder, then, that two researchers who are working on ways of defending against the future possibility of malicious attack assume that any unauthorised access to a quantum computer constitutes a catastrophic failure.

For that reason, their defense resembles the communications protocol for a paranoid spy: Only send out messages at prearranged and seemingly random intervals, have long average wait times between legitimate network connections, and fill all the unused network time with decoy transmissions.

By spreading out network connections over random intervals in time, the researchers - Daniel Lidar, an associate professor in electrical engineering, chemistry and physics at the University of Southern California and Lian-Ao Wu, a research associate in the Chemical Physics Theory Group at the University of Toronto - have shown quantum computer scientists how they can reduce the chance of a successful attack but still keep the performance advantages promised by quantum computing.

"We would not want to use this method against any threat beside malware, because it is inefficient," Lidar said in an interview with SecurityFocus. "We are taking the network down for a long period of time."

Quantum computers are only taking their first toddler steps in the world of computer science. While a research topic in physics for more than 20 years, quantum computing has only recently moved from its theoretical underpinnings to actually being demonstrated in the lab.

The promise of such computers, however, is nothing short of astonishing. Many problems that "blow up" on a classical computer system, such as finding the prime factors of a large number, can theoretically be easily solved on a quantum computer. Other aspects of a quantum information system allow for more interesting possibilities, such as the secure transmission of encryption keys over quantum networks.

For example, in conjunction with Harvard University and Boston University, internet service provider BBN Technologies built the DARPA Quantum Network, billed as the world's first quantum key distribution (QKD) network.

The project, funded by the Defense Advanced Research Projects Agency (DARPA), uses light particles, or photons, that are linked over a distance through the quantum mechanical property of entanglement to transmit key information in a way that any eavesdropping can be detected.

Yet, as such technologies mature and greater access is granted to researchers outside the core group of quantum computer scientists, the probability that such computers and systems will be attacked increases. The computers already have to be hardened against any interaction with the environment, to ward off the impact of even a single cosmic ray, which could pollute an ongoing quantum process and affect the outcome of an operation. The impact of an intelligent attacker is a more difficult problem.

"I want to maintain the quantum computer in a good state until, magically, the answers appear," said John Lowry, a principal scientist at internet service provider BBN Technologies and a member of that company's research team working on the DARPA Quantum Network. "Stray cosmic rays and things like that - if they interact with this stuff, then something changes and the computer crashes. The thought is that people could do that on purpose."